This invention relates to the preparation of ceramic materials or articles by the pyrolysis of vinyl- or allyl-containing preceramic silazane polymers wherein the vinyl- or allyl-containing preceramic silazane polymers are rendered infusible prior to pyrolysis by high energy radiation such as gamma rays or an electron beam. This method is especially suited for the preparation of ceramic fibers.
This invention also relates to a method of rendering preceramic silazane polymers infusible.
Ceramic materials have been prepared by the pyrolysis of various preceramic polymers in the prior art. Gaul in U.S. Pat. No. 4,312,970 (issued Jan. 26, 1982) obtained ceramic materials by the pyrolysis of preceramic silazane polymers prepared by reacting organochlorosilanes and disilazanes. The preceramic silazane polymers were pyrolyzed in an inert atmosphere without any separate treatment to render the silazane preceramic polymer infusible.
Gaul in U.S. Pat. No. 4,340,619 (issued July 20, 1982) obtained ceramic materials by the pyrolysis of preceramic silazane polymers prepared by reacting chlorine-containing disilanes and disilazanes. Fibers prepared from such preceramic silazane polymers were given a "mild heat treatment" in air before pyrolysis but there is no teaching that such a treatment rendered the fibers infusible.
Cannady in U.S. Pat. No. 4,540,803 (issued Sept. 10, 1985) obtained ceramic materials by the pyrolysis of preceramic silazane polymers prepared by reacting trichlorosilane and disilazane. The preceramic silazane polymers were not rendered infusible prior to pyrolysis to form ceramic materials.
Haluska in U.S. Pat. No. 4,546,163 (issued Oct. 8, 1985) prepared vinyl-containing polysilanes of the average formula (R.sub.2 Si)(RSi)(R'.sub.d (CH.sub.2 .dbd.CH)Si) where R was an alkyl radical containing 1 to 4 carbon atoms, R' was an alkyl radical containing 1 to 4 carbon atoms, a vinyl radical or a phenyl radical, d was 1 or 2 and where the polysilane contained 0 to 60 mole percent (R.sub.2 Si) units, 30 to 99.5 mole percent (RSi) units, and 0.5 to 15 mole percent (R'.sub.d (CH.sub.2 .dbd.CH)Si) units. Shaped articles prepared from such polysilanes could be rendered infusible prior to pyrolysis by UV treatment.
Bartos et al. in U.S. patent application Ser. No. 748,109, filed June 24, 1985, obtained infusible preceramic silazane polymers by treatment of the preceramic silazane polymer with a steam or a steam and oxygen mixture.
Lipowitz, in a copending U.S. patent application entitled "Infusible Preceramic Polymers via Plasma Treatment", obtained infusible preceramic polymer by treatment of the preceramic polymer with a plasma energy source. Both vinylcontaining and vinyl-free preceramic polymers were rendered infusible by plasma treatment. High eenrgy electrons interact with neutral gas molecules in the plasma thereby forming unique species such as metastable species, atoms, radicals, and ions. These unique species then interact with the preceramic polymer thereby rendering the preceramic polymer infusible.
Lutz et al., in a copending application entitled "Infusible Preceramic Polymers via Ultraviolet Irradiation", obtained infusible preceramic polymer compositions by treatment of the compositions with UV irradiation wherein the compositions contained vinyl- or allyl-containing preceramic polymers, mercapto compounds, and photoinitiators.
Yajima et al. in U.S. Pat. Nos. 4,220,600 (issued Sept. 2, 1980), 4,283,376 (issued Aug. 11, 1981), 4,342,712 (issued Aug. 3, 1982), and 4,399,232 (issued Aug. 16, 1983) disclosed the use of gamma ray or electron beam irradiation to cure preceramic modified polycarbosilane fibers prior to pyrolysis. Unmodified polycarbosilane is a polymer having a skeletal structure composed substantially of recurring carbosilane units of the formula ##STR1## The modified polycarbosilane of U.S. Pat. Nos. 4,220,600 and 4,283,376 are composed mainly of the structural units ##STR2## and also contain some boron in the skeletal polymer chain. The modified polycarbosilanes of U.S. Pat. Nos. 4,342,712 and 4,399,232 are block copolymers composed mainly of carbosilane units with titanoxane units of the formula --(--Ti--O--)--.
What has been newly discovered is a method of rendering certain preceramic silazane polymers infusible prior to pyrolysis by irradiation of the preceramic silazane polymers with high energy radiation sources such as gamma or electron beam irradiation. This method represents a significant advance in the art of preparing ceramic materials or articles, especially in the art of preparing ceramic fibers.